1. Field of the Invention
The present invention relates to a liquid crystal panel manufacturing method for manufacturing a plurality of liquid crystal panels by using one master glass substrate, a liquid crystal panel manufactured by the manufacturing method and a manufacturing system of the same.
2. Description of the Related Art
A display using a liquid crystal panel of an active matrix system prevents crosstalk by providing a switch for each pixel (picture element), the switch being turned OFF at the time of unselection to cut off a signal. Compared with a display using a liquid crystal panel of a simple matrix system, this display shows a better display characteristic. Especially, a liquid crystal display using TFT (Thin Film Transistor) as a switch shows a display characteristic as excellent as that of CRT (Cathode-Ray Tube), because of high driving performance of TFT.
Generally, the liquid crystal panel has a structure where a liquid crystal is enclosed between two transparent substrates. A counter electrode, a color filter, an orientation film, and so on, are formed on one of two opposing surfaces of the transparent substrates. TFT, a pixel electrode, an orientation film, and so on, are formed on the other surface. Also, polarizing plates are stuck to surfaces opposite the opposing surfaces of the respective transparent substrates. These two polarizing plates are arranged, for example, so that polarization axes of the polarizing plates can be orthogonal to each other. In this arrangement, a light is transmitted in a state of no electric field application. In a state of electric field application, a light shielding mode, i.e., a normally white mode, is set. Conversely, when the polarization axes of the two polarizing plates are in parallel with each other, a normally black mode is set. Hereinafter, a transparent substrate having TFT and a pixel electrode, or a transparent substrate having TFT and a pixel electrode formed therefrom, is referred to as TFT substrate. A transparent substrate having a counter electrode and a color filter is referred to as CF substrate.
Recent years have seen a gradual increase in size of the liquid crystal panel of an active matrix type, which is used in a notebook personal computer (referred to as “PC”, hereinafter), and a desktop PC, a work station or the like.
In manufacturing of a liquid crystal panel, generally, a large substrate called master glass is used. The master glass substrate is plotted into a plurality of liquid crystal panel forming regions. TFT, a pixel electrode, and so on, are formed in each region, and then a spacer is dispersed on the master glass substrate (TFT substrate). The master glass substrate and a CF substrate are joined with the spacer between. Subsequently, the master glass substrate is divided to form individual liquid crystal panels. With enlargement of the liquid crystal panel, a size of the master glass substrate has a tendency to be increased year by year. Also, in order to reduce manufacturing costs, the number of liquid crystal panels manufactured by using one master glass substrate (the number of yielded pieces) has been increased.
Table 1 below shows correspondence between a manufacturing line generation of a liquid crystal panel of an active matrix system and a size of a master glass substrate. FIG. 1 shows comparison in size among master glass substrates of respective generations.
TABLE 1Linegenera-SubstratetionsizeType 10Type 11Type 12Type 13Type 15Phase 1300 × 4002 pieces2 pieces1 piece1 piece1 piecemmyieldedyieldedyieldedyieldedyieldedPhase 2360 × 4654 pieces2 pieces2 pieces2 pieces1 piecemmyieldedyieldedyieldedyieldedyieldedPhase400 × 5004 pieces2 pieces2 pieces2 pieces2.5mmyieldedyieldedyieldedyieldedPhase 3550 × 6506 pieces4 pieces4 piecesmmyieldedyieldedyieldedPhase600 × 7206 pieces4 pieces3.5mmyieldedyieldedPhase 4960 × 1000129 piecesmmpiecesyieldedyielded
As shown in Table 1, in the manufacturing line of phase 1, a size of the master glass substrate is 300×400 mm, and two liquid crystal panels of type 10 (length of a diagonal is 10.4 inch) or type 11 (length of a diagonal is 11.4 inch) can be simultaneously formed. On the other hand, in the manufacturing line of phase 4 currently under studies by makers, the master glass substrate has a size of 960×1000 mm, and an area 8 times as large as that of the master glass substrate of phase 1. With the master glass substrate of phase 4, twelve liquid crystal panels of type 13 (length of a diagonal is 13.3 inch) or type 14 (length of a diagonal is 14.1 inch) can be simultaneously manufactured.
Recent years have also seen diversification of demands for liquid crystal panels. At first, the liquid crystal panel was mainly used as a display for a notebook PC. Then, there has been expansion year by year regarding markets for a large liquid crystal panel used as a display for a desktop PC or a work station, a medium or a small liquid crystal panel used for a mobile equipment such as a mobile communication equipment or a portable information equipment, and a liquid crystal panel used for a video equipment such as television (TV), video (VTR), a digital camera or the like.
Conventionally, the manufacturing line of a liquid crystal panel has been constructed basically for the purpose of providing a liquid crystal panel having a specified dimension. For example, as shown in FIGS. 2 and 3, in the manufacturing line of phase 1, a size of a master glass substrate is decided with a view to yielding two pieces for the liquid crystal panel of type 10. The manufacturing line is constructed in accordance with this master glass substrate. The following manufacturing lines are similarly constructed: the manufacturing line of phase 2 for yielding four pieces of the liquid crystal panel of type 10; the manufacturing line of phase 2.5 for yielding four pieces of the liquid crystal panel of type 10 or 11; the manufacturing line of phase 3 for yielding four pieces of the liquid crystal panel of type 12 (length of a diagonal is 12.1 inch); and the manufacturing line of phase 3.5 for yielding six pieces of the liquid crystal panel of type 13. Also, the manufacturing line of phase 4 is constructed with a view to yielding twelve pieces of the liquid crystal panel of type 13 or 14, or yielding four to six pieces of the liquid crystal panel of type 15 or bigger.
The inventors of this application consider that the following three problems are inherent in the conventional manufacturing method of the liquid crystal panel.
The first problem is great fluctuation in productivity caused by a dimension of the liquid crystal panel. FIG. 4 shows a relationship between a panel size of the manufacturing line of phase 3 (size of the master glass substrate is 550×650 mm) and the number of yielded pieces. In the manufacturing line of phase 3, six pieces of the liquid crystal panel of type 11 or 12 are yielded; four pieces of the liquid crystal panels of types 13 to 15 are yielded; two pieces of the liquid crystal panels of types 16 to 19 are yielded; and one piece of the liquid crystal panel of types 20 to 24 is yielded.
Table 2 below shows dependence of an effective substrate utilization factor reflecting productivity on the number of panel pieces yielded and a panel dimension.
TABLE 2Panel dimension(type)Number of yieldedEffective substrate(or diagonal inch)piecesutilization factorType 126 pieces yielded0.86Type 134 pieces yielded0.67Type 154 pieces yielded0.87Type 162 pieces yielded0.51Type 192 pieces yielded0.72Type 201 piece yielded0.40Type 241 piece yielded0.57
Herein, an area of the master glass substrate excluding a handling region of an edge part is set as a substrate effective area, and an area of a display region of the liquid crystal panel is set as a panel area. Then, effective utilization area=panel area×number of yielded pieces, and effective substrate utilization factor=effective utilization area/substrate effective area are defined.
As can be understood from Table 2, even if panel sizes are changed from type 16 to type 19, the number of liquid crystal panels to be simultaneously manufactured is still two. Accordingly, an effective substrate utilization factor fluctuates in a range of 0.51 to 0.72. In other words, in a given manufacturing line, there is a panel size having a maximum effective substrate utilization factor with the fixed number of yielded pieces. For example, in the case of the manufacturing line of phase 3, a panel size having a maximum effective substrate utilization factor is type 12 with the number of yielded pieces set to 6; type 15 with the number of yielded pieces set to 4; type 19 with the number of yielded pieces set to 2; and type 24 with the number of yielded pieces set to 1. Among these, a highest effective substrate utilization factor is 0.86 of type 12 with the number of yielded pieces set to 6, and a lowest effective substrate utilization factor is 0.4 of type 20 with the number of yielded pieces set to 1. This means that the conventional method exhibits fluctuation twice as large or more, because an effective substrate utilization factor fluctuates in a range of 0.4 to 0.87 depending on the sizes of liquid crystal panels to be manufactured.
The second problem is inability to deal with diversification of products, which is caused by enormous investments made in the manufacturing line for liquid crystal panels. Recent years have seen gradually expanded use of liquid crystal panels for a display of a notebook (including sub-notebook) PC, a desktop PC or a work station, a display of a mobile equipment, a video equipment, and so on. Conventionally, however, a basic idea has been the following: {circle around (1)} a liquid crystal panel having a specified size is manufactured in a specified manufacturing line; and {circle around (2)} a specified variety is fed at a specified lot. Accordingly, in order to deal with diversified liquid crystal panels, a plurality of manufacturing lines must be constructed according to sizes and varieties of liquid crystal panels. Conventionally, manufacturing lines have been constructed to match liquid crystal panels to be manufactured, for example in a manner that a liquid crystal panel is manufactured for a notebook PC in a first manufacturing line, a liquid crystal panel is manufactured for a mobile equipment and a video equipment in a second manufacturing line, and a liquid crystal panel is manufactured for a monitor in a third manufacturing line.
It was relatively easy to construct manufacturing lines according to sizes or varieties of liquid crystal panels when there were not many kinds of products. From now on, however, with a great increase in size of a master glass substrate and diversification of products, construction of a manufacturing line for each product will bring about an enormous increase in plant and equipment investments. Thus, it will be difficult to deal with diversified products.
The third problem of the conventional method is inability to deal with changes in market demands. For example, around 1994, each maker of a liquid crystal panel predicted that a size of a liquid crystal panel for a notebook PC would be type 10, and accordingly constructed a manufacturing line of phase 2 with a view to yielding four pieces of the liquid crystal panel of type 10. Less than a year, however, a mainstream size of the liquid crystal panel for a notebook PC changed to type 11. As a result, almost no manufacturing lines which had been constructed had capability of dealing with the new need, the line was changed to type 11 with the number of yielded pieces set to 2. Thus, productivity was reduced by half.
In the next year, 1995, since a mainstream size of the liquid crystal panel changed to type 12, a specially constructed manufacturing line of phase 2.5 became one for manufacturing a liquid crystal panel of type 12 with the number of yielded pieces set to 2. Also, in this case, productivity was reduced by half.